U.S. patent number 3,941,562 [Application Number 05/367,081] was granted by the patent office on 1976-03-02 for corrosion inhibition.
This patent grant is currently assigned to Calgon Corporation. Invention is credited to William Robert Hollingshad.
United States Patent |
3,941,562 |
Hollingshad |
March 2, 1976 |
Corrosion inhibition
Abstract
Use of low molecular weight polymer and phosphate compositions
to inhibit the corrosion of metals by oxygen-bearing waters.
Inventors: |
Hollingshad; William Robert
(Bethel Park, PA) |
Assignee: |
Calgon Corporation (Pittsburgh,
PA)
|
Family
ID: |
23445858 |
Appl.
No.: |
05/367,081 |
Filed: |
June 4, 1973 |
Current U.S.
Class: |
422/16; 252/180;
148/251; 252/181; 252/389.2; 252/387; 422/18 |
Current CPC
Class: |
C23F
11/08 (20130101) |
Current International
Class: |
C23F
11/08 (20060101); C23F 011/16 (); C23F
011/10 () |
Field of
Search: |
;252/389A,389R,387,180,181,390 ;21/2.5A,2.5R,2.7A,2.7R
;210/58,59 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Sebastian; Leland A.
Assistant Examiner: Gluck; Irwin
Attorney, Agent or Firm: Anderson, Jr.; Rudolph J. Westlake;
Harry E. Katz; Martin L.
Claims
I claim:
1. A method of inhibiting the corrosion of metals in a water system
which comprises maintaining in the water of said system at least
about 10 ppm of a composition comprising a polyacrylamide having a
molecular weight of from about 500 to about 10,000 and a source of
orthophosphate.
2. A method as in claim 1 wherein the ratio of polymer to phosphate
is from about 20:1 to about 1:1 by weight.
3. A method as in claim 2 wherein the ratio of polymer to phosphate
is from about 5:1 to about 2:1 by weight.
4. A method as in claim 1 which further contains zinc.
5. A method as in claim 1 which further comprises a member selected
from the group consisting of benzotriazole and
mercaptobenzothiazole.
Description
BACKGROUND OF THE INVENTION
This invention relates to the inhibition of corrosion in water
systems which utilize oxygen-bearing waters.
More particularly, this invention relates to the use of
compositions comprising low molecular weight polymers and
phosphates to inhibit the corrosion of metals in water systems
which contain oxygen-bearing waters.
Oxygen corrosion is, of course, a serious problem in any
metal-containing water system. The corrosion of iron and steel is
of principal concern because of their extensive use in many types
of water systems. Copper and its alloys, aluminum and its alloys,
and galvanized steel are also used in water systems and are subject
to corrosion. I have discovered corrosion inhibitors which will
inhibit oxygen corrosion in water systems containing such
metals.
SUMMARY OF THE INVENTION
I have found that compositions comprising low molecular weight
polymers and phosphates are effective corrosion inhibitors.
Suitable polymers include water-soluble salts of acrylates and
methacrylates, unhydrolyzed or partially hydrolyzed acrylamides,
and acrylamidomethyl propane sulfonates. The polymers may be homo-,
co-, or ter- polymers of any of the aforementioned polymers and may
have a molecular weight of from about 500 to about 10,000. The
preferred molecular weight, however, is about 1,000.
Suitable phosphates include any source of the ortho-
PO.sub.4.sup..sup.-3 ion as, for example, phosphoric acid, mono, di
and tri sodium phosphate, or mono, di and tri sodium
polyphosphate.
The corrosion-inhibiting compositions can contain a ratio of
polymer to phosphate of from about 20:1 to about 1:1 by weight. The
preferred ratio, however, is from about 5:1 to 2:1 by weight. These
compositions will effectively inhibit corrosion of metals when
maintained in a water system at a concentration of at least about
10 ppm at the above ratios and, preferably, about 30 ppm. Maximum
concentrations are determined by the economic considerations of the
particular application.
It may, of course, be desirable to add zinc to the compositions of
this invention for certain applications. The zinc ion may be
supplied in many ways. For example, it may be added by utilizing a
water-soluble zinc salt, such as, zinc chloride, zinc acetate, zinc
nitrate, or zinc sulfate or it may be supplied by adding powdered
zinc to a solution of the composition.
Compounds such as benzotriazole or mercaptobenzothiazole may also
be added to the final formulation in varying amounts to improve its
usefulness in a wider variety of industrial applications where both
steel and copper are present in the same system.
The following tables show the results of experiments which
demonstrate the effectiveness of the compositions of this invention
in inhibiting metallic corrosion. These tests were run in synthetic
Pittsburgh water. Steel electrodes were used in polarization test
cells with the initial pH at 7.0. Inhibitor concentrations were
calculated on the basis of 100 percent active material. The amount
of corrosion that had taken place was determined from the current
density at the intersection of an extrapolation of the so-called
"Tafel" portion of the anodic polarization curve with the
equilibrium or "mixed" potential value, usually referred to as the
corrosion potential, "E.sub.corr." Application of Faraday's Law
allows a computation of a direct mathematical relationship between
the current density at E.sub.corr, expressed in amperes per square
centimeter and a more useful corrosion rate expression such as
milligrams of steel consumed per square decimeter of surface per
day (m.d.d.) and mils per year (m.p.y.). This relationship is such
that a current density value of 4.0 .times. 10.sup..sup.-7
amperes/cm.sup.2 = 1.0 mg/dm.sup.2 /day. Further, the m.p.y. value
is calculated from the formula: m.p.y. = m.d.d. .times.
(1.44/density), using a density value of 7.87 g/cm.sup.3 for
steel.
The following tables illustrate the synergistic effect of a
composition comprising sodium polyacrylate and phosphoric acid as a
corrosion inhibitor in tests run at 35.degree.C.
Table 1 ______________________________________ Dosage Corrosion
Rate Inhibitor System (mg/l) (mdd)
______________________________________ Control 0 100 Sodium
Polyacrylate (molecular weight .about. 1,000) 30 78 Phosphoric Acid
5 83 Sodium Polyacrylate + Phosphoric Acid 30 + 5 4
______________________________________ Table 2 Dosage Corrosion
Rate Inhibitor System (mg/l) (mdd)
______________________________________ Control 0 100 Sodium
Polyacrylate (molecular weight .about. 1,000) 60 48 Phosphoric Acid
3 73 Sodium Polyacrylate + Phosphoric Acid 60 + 3 10
______________________________________ Table 3 Dosage Corrosion
Rate Inhibitor System (mg/l) (mdd)
______________________________________ Control 0 100 Sodium
Polyacrylate (molecular weight .about. 1,000) 60 48 Phosphoric Acid
9 8 Sodium Polyacrylate + Phosphoric Acid 60 + 9 2
______________________________________
* * * * *